op-amp parameters
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>>I find that most of
>>my requirements can be met by a few op amps I keep in stock. It is when
>>those fall short on some parameter that it is time to go shopping again.
>Thanks Tracy and Dennis for your comments. I'll bet we all would learn
>something if we knew which op-amps Tracy keeps in stock, and a brief
>comment on why for each one! Tracy, could we see your op-amp list please?
>Dennis also if possible. I think these would be good general guidelines.
>Any other comments? Thanks!
>Steve
Hi Steve,
The class of op-amps I use most would be, "precision, single supply,
micropower". I use these for interfaces to sensors that for the most part
are operating at or below 2000 hertz frequency. There are several
different classes of op amps. For example, audio ampilfiers or amplifiers
for high-speed or power instrumentation would use a different class of
op-amps. In general, the faster an op-amp, the more power supply current
it draws.
That said, my favorites are the LT1077 (single) and LT1078 (dual) for
general purpose use. 50 micoamps supply current per amplifier, 70
microvolts max input offset, output and input include ground, stable.
200khz gain-bandwidth.
The LM358 (or the LM324) are jellybean single supply capable op-amps, at 2
millivolts max input offset. 1mhz gain-bandwidth. It is a good choice for
lots of less demanding projects, and it is dirt cheap and always available.
For super precision, I use the LTC1051 or the LTC1047, which are chopper
stablized amplifiers. The offsets are less than 5 microvolts and drifts
less than 50nV/'C. That would be the front end for a DC amplifier.
For special purposes, I keep the LMC6062 (precision rail to rail output
CMOS) and the LMC6482 (rail to rail input and output CMOS). The
rail-to-rail inputs and outputs are very useful in single supply circuits,
and the CMOS inputs have very high input impedances for things like pH
probes. The LMC6482 makes a good comparator. I still have lots of the
original CMOS op-amp, the CA3130, on hand, but don't use that much any more
in favor of the newer ones that operate at much lower supply current and
with greater accuracy.
My most recent shopping trip was for a rail-to-rail input and output op-amp
that would operate off of a 2.5 volt power supply at less than 100
microamps supply current, and have < 100 microvolts offset, slew to full
scale (turn on completely) within 1 millisecond. I compared products from
National, TI, Maxim, and Linear Tech, and had no trouble getting samples.
I ended up with the LT1490A, but actually getting ahold of a tube of parts
to complete the project was a big chore. All of these low voltage parts
are on allocation, because the cell phone and gadget companies are gobbling
them up and leaving zilch in the distribution channels.
The LT1101 is an instrumentation amplifier that has strapped gains of x10
or x100. It is like the LT1078 op-amp, but preconfigured as a differential
amplifier (2-op-amp circuit). Other companies like Burr-Brown have similar
parts. These are very useful for things like strain gages or pressure
transducers.
Many circuits require a voltage reference. I use the LM385 a lot. As
voltage regulators go, the LP2950 is one of the most stable and can almost
qualify as a reference. The TLE2425 from Texas Instruments is a very
useful part that supplies a 2.5 volt psuedo-ground that can make some dual
supply circuits work in a single-supply system.
My all-time favorite op-amp is the National LM10. It was in my opinion the
crowning acheivement of the guru's guru, Bob Widlar, who also designed the
original '709 op amp, as well as the original '741. Legend has it that he
designed the LM10 while on extended vacation in Puerto Vallarta. While the
'741 has been superceded by wave after wave of new technology, the LM10
stands by itself, unconventional, and is still in production. It is a
single supply or floating op-amp that can operate down to a 1.1 volt total
supply, and it includes both an op-amp and a 0.2 volt reference in the same
package. The combination makes it extremely useful in signal conditioning
circuits and in things like 4-20 milliamp converters. Start with Bob
Widlar's original paper (very readable) in National App-note AN211.
As in programming, one of the best ways to learn about op-amps is to look
at circuits that have been designed by experts. Remember that the origin
of the op-amp is as an analog computer, and it is programmed by its
circuitry. I like the National Ap-notes, and The Art of Electronics by
Horowitz and Hill, because they talk about both the how and the why. The
choice of which op-amp to use comes down to narrowing the choice to meet
the main requirements, and then checking off parameters one by one to see
if there are bugs that will come back to bite you later. And testing,
analysis, testing. Just like programming.
I hope that helps!
-- Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
>>my requirements can be met by a few op amps I keep in stock. It is when
>>those fall short on some parameter that it is time to go shopping again.
>Thanks Tracy and Dennis for your comments. I'll bet we all would learn
>something if we knew which op-amps Tracy keeps in stock, and a brief
>comment on why for each one! Tracy, could we see your op-amp list please?
>Dennis also if possible. I think these would be good general guidelines.
>Any other comments? Thanks!
>Steve
Hi Steve,
The class of op-amps I use most would be, "precision, single supply,
micropower". I use these for interfaces to sensors that for the most part
are operating at or below 2000 hertz frequency. There are several
different classes of op amps. For example, audio ampilfiers or amplifiers
for high-speed or power instrumentation would use a different class of
op-amps. In general, the faster an op-amp, the more power supply current
it draws.
That said, my favorites are the LT1077 (single) and LT1078 (dual) for
general purpose use. 50 micoamps supply current per amplifier, 70
microvolts max input offset, output and input include ground, stable.
200khz gain-bandwidth.
The LM358 (or the LM324) are jellybean single supply capable op-amps, at 2
millivolts max input offset. 1mhz gain-bandwidth. It is a good choice for
lots of less demanding projects, and it is dirt cheap and always available.
For super precision, I use the LTC1051 or the LTC1047, which are chopper
stablized amplifiers. The offsets are less than 5 microvolts and drifts
less than 50nV/'C. That would be the front end for a DC amplifier.
For special purposes, I keep the LMC6062 (precision rail to rail output
CMOS) and the LMC6482 (rail to rail input and output CMOS). The
rail-to-rail inputs and outputs are very useful in single supply circuits,
and the CMOS inputs have very high input impedances for things like pH
probes. The LMC6482 makes a good comparator. I still have lots of the
original CMOS op-amp, the CA3130, on hand, but don't use that much any more
in favor of the newer ones that operate at much lower supply current and
with greater accuracy.
My most recent shopping trip was for a rail-to-rail input and output op-amp
that would operate off of a 2.5 volt power supply at less than 100
microamps supply current, and have < 100 microvolts offset, slew to full
scale (turn on completely) within 1 millisecond. I compared products from
National, TI, Maxim, and Linear Tech, and had no trouble getting samples.
I ended up with the LT1490A, but actually getting ahold of a tube of parts
to complete the project was a big chore. All of these low voltage parts
are on allocation, because the cell phone and gadget companies are gobbling
them up and leaving zilch in the distribution channels.
The LT1101 is an instrumentation amplifier that has strapped gains of x10
or x100. It is like the LT1078 op-amp, but preconfigured as a differential
amplifier (2-op-amp circuit). Other companies like Burr-Brown have similar
parts. These are very useful for things like strain gages or pressure
transducers.
Many circuits require a voltage reference. I use the LM385 a lot. As
voltage regulators go, the LP2950 is one of the most stable and can almost
qualify as a reference. The TLE2425 from Texas Instruments is a very
useful part that supplies a 2.5 volt psuedo-ground that can make some dual
supply circuits work in a single-supply system.
My all-time favorite op-amp is the National LM10. It was in my opinion the
crowning acheivement of the guru's guru, Bob Widlar, who also designed the
original '709 op amp, as well as the original '741. Legend has it that he
designed the LM10 while on extended vacation in Puerto Vallarta. While the
'741 has been superceded by wave after wave of new technology, the LM10
stands by itself, unconventional, and is still in production. It is a
single supply or floating op-amp that can operate down to a 1.1 volt total
supply, and it includes both an op-amp and a 0.2 volt reference in the same
package. The combination makes it extremely useful in signal conditioning
circuits and in things like 4-20 milliamp converters. Start with Bob
Widlar's original paper (very readable) in National App-note AN211.
As in programming, one of the best ways to learn about op-amps is to look
at circuits that have been designed by experts. Remember that the origin
of the op-amp is as an analog computer, and it is programmed by its
circuitry. I like the National Ap-notes, and The Art of Electronics by
Horowitz and Hill, because they talk about both the how and the why. The
choice of which op-amp to use comes down to narrowing the choice to meet
the main requirements, and then checking off parameters one by one to see
if there are bugs that will come back to bite you later. And testing,
analysis, testing. Just like programming.
I hope that helps!
-- Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
Comments
Thanks for the very informative comments. I've got quite a few gaps in my
analog design knowledge (not to mention other gaps) and comments like
Tracy's I find especially useful. I hope others have benefitted as much as
I have from this thread. Any other comments from the other gurus would
always be appreciated. Thanks again!
Steve
Steve Roberts: sroberts@s...